Electroluminescent device



y 1963 R. c. DEMMY 3,

ELECTROLUMINESCENT DEVICE Filed July 19, 1960 INVENTOR. RUBERT E- DEMMY ATTOi/VEY United States Patent 3,096,458 ELECTROLUMKNESCENT DEVICE Robert C. Demmy, Lancaster, Pa, assignor to Radio Corporation of America, a corporation of Delaware Filed July 19, 1960, Ser. No. 43,930 7 Claims. (Cl. 313-108) This invention relates to electroluminescent devices. In particular, this invention relates to an improved construction of an economical, sealed housing assembly for such devices.

One of the problems that has been encountered in the manufacture of an electroluminescent panel is that the useful life of the panel is limited by the presence of moisture within the panel. Therefore, it is desirable that the panel be sealed from moisture so that its life will not be shortened by the penetration of moisture to the active elements of the panel. A particular example of extreme moisture conditions is when a panel is designed to be used under the high humidity conditions of a bath room in a home.

Another problem in the construction of an electroluminescent assembly is that of electrical arcing between the edges of the electrodes between which the electroluminescent phosphor is disposed. This problem is known as edge arcing. The device is ruined when edge arcing occurs. Edge arcing may occur between the two electrically energized electrodes of the device, in some instances, or edge arcing may occur from one electrode to a metal support case.

A still further problem in the design of an electroluminescent panel assembly is that of cost. In particular, many electroluminescent panel sizes and shapes are desired for particular uses. In order to manufacture these many sizes and shapes, while utilizing a low cost design, a wide tolerance, i.e. one in which the dimensions of the device need not be accurately controlled, must be used in order to reduce the cost of assembling the device.

It is therefore an object of this invention to provide an improved electroluminescent device.

It is a further object of this invention to provide a novel electroluminescent device characterized by low cost, efiicient moisture sealed structure and freedom from edge arcing.

These and other objects are accomplished in accordance with this invention by providing an electroluminescent device which is sealed between a glass face plate and a novel metallic back plate. The housing for the electroluminescent device is designed so that the area of possible moisture penetration is at a minimum. To this end, the back plate includes a deep well that is positioned adjacent to the periphery of the face plate so that a good seal may be made in this area while permitting wide tolerances between the various assemblies. The back plate is so designed that edge arcing, even with the wide tolerances, is eliminated.

The invention will be more clearly understood by reference to the accompanying single sheet of drawings, where- The single FIGURE is a sectional view of an electroluminescent panel in accordance with this invention.

Referring now to the drawing, there is shown an electroluminescent lamp 10 which comprises a transparent faceplate 12 which may be made of any material that is impervious to moisture and that is transparent to the radiations to be emitted by the device 10. Examples of such materials are glass and plastic. On the under side of the transparent face plate '12, there is positioned a transparent conductive coating 14 which may be made of a material such as tin oxide. The transparent conductive coating, which is transparent to the radiations to be emitted by the device 10, may be deposited on the glass plate 12 by any conventional means such as spraying. In the al- "ice tern-ative, the transparent conductive coating 14 may be formed of a thin evaporated layer of a material such as gold. On the transparent conductive coating 14 there is provided a layer 16 of a mixture of electroluminescent phosphor material and a binder. The electroluminescent phosphor material 16 may be of a material such as, for example, zinc sulfide or zinc sulphoselenide. The binder, which is mixed with the electroluminescent phosphor may be a material such as an epoxy resin or ethyl cellulose. The electroluminescent phosphor material, or mixture of materials, is properly activated to produce electroluminescent light of any desired color. On the layer of electroluminescent phosphor 16 there is a layer of dielectric material 17, for example barium titanate mixed with an epoxy resin, which is approximately a few thousands of an inch thick and which is used to prevent voltage breakdown, or arcing, through the electroluminescent phosphor 16. Depending upon the electrical properties of the phosphor and binder, the dielectric material 17 may be omitted. On the dielectric layer 17 is deposited a back electrode 18. If a transparent electrode 18 is desired, a thin evaporated layer may be applied to the layer 17. If an opaque electrode 13 is desired, a relatively thick and light reflective evaporated layer of aluminum may be used. The subasse'mbly so far described is normally formed by sequentially depositing the layers '14, 16, -17 and 18 onto the face plate 12.

When it is desired to insulate the envelope of the device from any electrical potential, an electrically insulating resin 20 is applied on the backing electrode 18. The electrically insulating resin 20 may be made of a material such as, for example, an epoxy resin of the thermal set type. The insulating resin may be deposited by spraying or pouring since it is in a liquid form before it has been cured by heating.

Positioned around, and slightly removed from the peripheral edges of the glass face plate 12 with its deposited layers, is a metallic back plate 22 which is impervious to moisture and which forms a portion of the envelope or housing for the device 10. It should be noted that the back plate 22 includes a peripherally arranged deep well portion 24. The back plate 22 may be a stamped metallic member, of approximately seven thousands of an inch in thickness, made of a material such as steel or a molded plastic plate. The deep well portion may extend inwardly from the edges of the back plate approximately one quarter of an inch and may be, for example, of an inch deep. The periphery of the glass 12 and its deposited layers extcnd substantially beyond the inner edge of the deep well 24- and the peripheral portion of the back plate 22 extends substantially perpendicularly to the plane of the glass face plate 12 and terminates substantially in the plane of the exposed face of the glass face plate 12. Thus, the minimum possible surface area of the device is exposed to possible moisture penetration. In other words, the only possible path of moisture entrance into the device is through the space between the face llate 12 and the upright portion 226 of the back plate 22.

The side Walls of the upright portion 26 are dimpled or depressed at spaced areas 36 and at an angle of approximately 45 so that the dimples or depressions 36 will, if the face plate 12 were mispositioned, contact only the top edge of the glass face plate 12. Thus, the electrodes 1 2 and 18 are at all times electrically insulated from the backing plate 22, by a space that exists between these electrodes and the adjacent back plate.

Extending from the electrodes 14 and 18 are a pair of leadin Wires 28 which extend to electrical connectors 30. The electrical connectors 30 extend through the backing plate 22 and are electrically insulated therefrom.

Positioned in the space existing between the face plate 12 with its various coatings 14, 16, 17, 18 and 2t) and in the deep well space, formed by the backing plate 22, is an insulating resin 32. The insulating resin 32 is selected for its good electrical insulating properties, its high resistance to moisture penetration, as well as the property of readily scaling to the glass plate 12 and the metallic backing member 22. A material which has been found to be suitable, and which includes all of these properties, is a thermal setting epoxy resin.

Thus, the electroluminescent lamp includes an effective moisture seal between the face plate 12, and the backing member 22. Since the glass face plate 12 and the metallic backing member 22 are both impervious to moisture, and since a minimum area exists between the face plate 12 and the back plate 22, and furthermore, since the insulating resin 32 is substantially impervious to moisture, the active parts of the electroluminescent lamps are sealed from any harmful effects of moisture.

It should be noted that the edges of the active elements .14, 16 and 18- overhang the walls of the deep well 24 and are spaced from the upright portion 26 of the backing plate 22. Thus, no edge arcing can occur either between the electrodes 14 and 13 or between the electrodes 14 or 18 and the backing plate 22. Thus, edge arcing is prevented by the electrode positions and by the presence of the electrically insulating material 32. It should also be noted that the glass plate 12, as Well as the electrodes deposited thereon, may be shifted toward or away from the upright walls 26 a substantial amount without contacting these Walls, such contact being prevented by the dimples 36. Thus, even if the plate 1-2 is shifted, only the glass contacts the dimpled or beveled edges 36 and the electrodes are prevented from contacting any portion of the back plate. Thus, the face plate 10 may be manufactured with wide tolerances, and the electrodes deposited over the complete surface thereof, and the assembly may be inserted into the space formed by the upright portions 26, without accurate control means being used, since the insulating resin 32 Will subsequently be inserted into this area to insulate the electrodes from the back plate. Because of this permissable wide toler-ance, the cost of an electroluminescent lamp made in accordance with this invention is substantially below that of lamps of other known configurations.

The device 1%) may be assembled by cutting a glass face plate 12 to any desired shape and size. The transparent electrode 14 may then be formed by spraying material over one entire surface of the glass plate 12. The electroluminescent phosphor with dielectric 16 and the dielectric layer 17 may then be deposited by spraying, and the back electrode 13 may be deposited by evaporation, also over the entire area of the face plate 12. The insulating resin 26 may then be deposited by spraying. As is obvious, no high cost controlling means is required for any of these manufacturing steps, since the particular laminated structures are deposited over one of the surfaces of the glass face plate 1-2 and no edge shields or stencils are required.

After a metallic back plate 22 has been formed to the desired size, i.e. somewhat larger than the glass plate 12 in the dimension in the plane of the plate 12, and the desired shape, the back plate 22 is filled with the thermal setting resin 32 and the face plate and its laminated elements is inverted and dropped into the structure formed by the backing plate 22. At this time the connectors 18 are connected to the lead-in terminals 36), Because the trough 26 encloses the periphery of the face plate 12, and is slightly larger in the dimension of the plane of the face plate 12, and because of the fact that the dimples or bevels 36 in the trough 26 contact, at most, only the glass, the positioning of the face plate 12 is automatic and need not be accurately controlled and thus, may be done With a minimum of manufacturing cost. Since the insulating resin 32 is in a liquid form, the weight of the face plate and electrodes will force an excess of resin out of the deep well. The resin 32 is a cured by oven drying at a temperature of approximately C. for a period of time of approximately 2 hours. Thus, the electroluminescent lamps manufactured in accordance with lapplicants invention do not require accurate parts or expensive machines for manufacture.

Applicants novel electroluminescent panels may take any desired shape or size, the only restriction being that the face plate 12 must be of substantially the same design or shape as the backing plate 22 and that the backing plate 22 be somewhat larger than the face plate 12. For rectangular panels, a size difference of approximately of an inch has been found suitable.

When desired, the backing plate 22 may be used as the electrode 18. Under these conditions, the plate 22 will have a potential applied thereto during operation of the panel 10, and the insulating resin 26' and backing electrode 18 are omitted.

What is claimed is:

1. A housing for an electroluminescent lamp comprising a transparent face plate, a back plate of substantially the same configuration as said face plate, said back plate having a well portion adjacent to the periphery of said back plate and means for sealing the periphery of said face plate to a portion of said back plate.

2. A housing for an electroluminescent lamp comprising a transparent face plate, a metallic back plate of substantially the same shape as said face plate, said back plate having a well portion surrounding the periphery of said face plate, and being cup-shaped to receive said face plate, means for sealing said face plate to the inner surface of said cup-shaped back plate, and a peripheral well in said back plate receiving said sealing means.

3. An electroluminescent lamp comprising an electroluminescent phosphor, a transparent conductor on one side of said phosphor, and a conductive layer on the other side of said phosphor, a housing for said lamp, said housing comprising a transparent face plate on said transparent conductor, an insulating coating on said conductive layer and a metallic back plate on said insulating coating, and said housing defining a space insulating the peripheral edges of said conductor and said transparent conductor.

4. An electroluminescent lamp comprising a light-transparent plate, a transparent first conductor on said plate, an electroluminescent phosphor means on said transparent conductor, a second conductor on said electroluminescent phosphor means, an electrically insulating coating on said second conductor, a metallic back plate, one surface of said insulating coating being positioned on said metallic back plate, said back plate including a peripherally positioned well, whereby the peripheral edges of said conductors are spaced from said back plate.

5. An electroluminescent lamp comprising a transparent face plate, a laminated structure in the order recited of a transparent conductor, an electroluminescent phosphor, a conductor and an insulator on said face plate, a back plate having a portion extending in a plane parallel with said plate and generally of the same configuration as said face plate, said back plate having said insulator positioned thereon, said back plate being larger than said face plate in the dimension of said plane, said back plate including a peripheral portion extending substantially normal to said plane to encompass the periphery of said face plate, said back plate further including a well portion extending from said peripheral portion inwardly beyond said face plate, whereby said electrodes are disposed above and spaced from said back plate, and a sealing resin in said well portion and extending from said face plate to said peripheral portion of said back plate.

6. A housing for an electroluminescent lamp comprising a light transparent member, a backing member having a portion of substantially the same shape as said transparent member, a peripheral portion of said backing member encompassing the periphery of said transparent member, and said backing member including a deep well portion positioned between said first named portion and said peripheral portion.

7. An electroluminescent lamp comprising a backing member, a transparent face, said backing member having cup-shaped walls for receiving the edges of said face, said backing member having a centrally positioned portion that is raised above the portion of said backing member that is closely [adjacent to said walls, at least one electrode and an electroluminescent phosphor on said face,

said face being positioned upon said raised portion Where- 10 by the edges of said face overhang said portion that is References Cited in the file of this patent UNITED STATES PATENTS Spielman Aug. 30, 1955 Destriau May 5, 1959 FOREIGN PATENTS Great Britain Nov. 16, 1955 

3. AN ELECTROLUMINESCENT LAMP COMPRISING AN ELECTROLUMINESCENT PHOSPHOR, A TRANSPARENT CONDUCTOR ON ONE SIDE OF SAID PHOSPHOR, A CONDUCTIVE LAYER ON THE OTHER SIDE OF SAID PHOSPHOR, A HOUSING FOR SAID LAMP, SAID HOUSING COMPRISING A TRANSPARENT FACE PLATE ON SAID TRANSPARENT 